Processes of producing ethanol from starch-containing material are well-known in the art and used commercially today. The production of ethanol as a bio-fuel has become a major industry, with in excess of 21 billion gallons of ethanol being produced worldwide in 2012.
When producing ethanol, starch is conventionally converted into dextrins using a liquefying enzyme (e.g., Bacillus alpha-amylase) at temperatures above the initial gelatinization temperature of starch. The generated dextrins are hydrolyzed into sugars using a saccharifying enzyme (e.g., glucoamylase) and fermented into the desired fermentation product using a fermenting organism such as a yeast strain derived from Saccharomyces cerevisiae. Typically hydrolysis and fermentation are done in a simultaneous saccharification and fermentation (SSF) step.
Another type of process is also used commercially today. Starch is converted into sugars by enzymes at temperatures below the initial gelatinization temperature of the starch in question and converted into ethanol by yeast, typically derived from Saccharomyces cerevisiae. This type of process is referred to as a raw starch hydrolysis (RSH) process, or alternatively a “one-step process” or “no cook” process.
Yeast which are used for production of ethanol for use as fuel, such as in the corn ethanol industry, require several characteristics to ensure cost effective production of the ethanol. These characteristics include ethanol tolerance, low by-product yield, rapid fermentation, and the ability to limit the amount of residual sugars remaining in the ferment. Such characteristics have a marked effect on the viability of the industrial process.
Yeast of the genus Saccharomyces exhibit many of the characteristics required for production of ethanol. In particular, strains of Saccharomyces cerevisiae are widely used for the production of ethanol in the fuel ethanol industry. Strains of Saccharomyces cerevisiae that are widely used in the fuel ethanol industry have the ability to produce high yields of ethanol under fermentation conditions found in, for example, the fermentation of corn mash. An example of such a strain is the yeast, used in the commercially available ethanol yeast product, sold under the trade named “ETHANOL RED™” and is available from Fermentis (A Lesaffre Division).
Strains of Saccharomyces cerevisiae are used in the fuel ethanol industry to ferment sugars such as glucose, fructose, sucrose and maltose to produce ethanol via the glycolytic pathway. These sugars are obtained from sources such as corn and other grains, sugar juice, molasses, grape juice, fruit juices, and starchy root vegetables and may include the breakdown of cellulosic material into glucose.
Although strains of Saccharomyces cerevisiae currently used in the fuel ethanol industry are well suited to ethanol production, there is an increasing need for improvements in the efficiency of ethanol production owing to the increased demand for ethanol as a fuel, and the increased availability of starch in new strains of corn.
There is therefore a need for new strains of Saccharomyces capable of improving the efficiency of ethanol production in industrial scale fermentation.
Further, despite significant improvement of ethanol production processes over the past decade there is still a desire and need for providing further improved processes of producing ethanol from starch-containing material that, e.g., can provide a higher ethanol yield.